The shortage of water resources and related ecological crises due to climate change make the drought resistance of crops an important research topic. As a plant stress hormone, abscisic acid (ABA) plays an important role in drought stress response. Abscisic acid is synthesized from the 2-C-methyl-D-erythritol-4-phosphate (MEP) pathway. Through binding with its receptor, ABA controls stomatal closure by a series of signal transductions and/or regulates stress-related gene expression through other pathways. Alfalfa (Medicago sativa) is a high-performing legume that is widely cultivated for forage. Under conditions of drought stress, ABA accumulates in alfalfa and is closely related to vegetative protein storage in the tap root, gene expression and a range of osmolyte responses. Research on the relationship between ABA and drought resistance in alfalfa is under development. This research will assist understanding drought resistance mechanisms in alfalfa and will have profound influences on the breeding of alfalfa cultivars.